An electrically connecting structure such as an interconnection for connecting elements between semiconductor devices is becoming more critical as the sizes of the devices are scaled down. Typically, the interconnection or other electrically conducting elements are widely used for providing specific conducting paths in an electrical circuit. In the process of forming the electrical conducting structure over an underlying layer, it is important that the surface of the underlying layer be free of any contamination, such as moisture, particles or oxides. Further, the surface of the underlying layer must be planar for subsequent layer deposition.
Tungsten (W) is one of the common materials used in the formation of an electrical conducting structure. Before forming a tungsten layer over an underlying layer having an etched hole, a glue layer composed of titanium (Ti) is sputtered on the surface of the underlying layer and on the walls of the hole. Through chemical vapor deposition (CVD) or PVD, a titanium nitride (TiN) layer is formed on the glue layer to act as a barrier layer. A rapid thermal annealing step is subsequently employed after the barrier layer is formed.
Next, a tungsten layer is deposited over the TiN layer by CVD or PVD. The tungsten is etched back to leave tungsten only within the hole to form a tungsten plug. The reaction material for forming the tungsten layer includes WF.sub.6 and SiH.sub.4. Fluorine will be generated during this reaction. The fluorine contamination will remain on the tungsten layer and the glue layer when the tungsten layer is etched back. When the wafer is taken out of the etching chamber, the fluorine reacts with air or moisture to form undesirable precipitate on the surface of the tungsten layer and the glue layer. The precipitate presents bridging concerns in subsequent metallization.
The conventional method of dealing with the precipitate involves using a wet chemical to strip the precipitate. Next, an argon (Ar) plasma is used to prevent future formation of precipitate. This method involves two steps that adds to the complexity and cost of manufacturing semiconductor devices.
What is required is a simpler, less costly method of preventing formation of undesired precipitate. Prevention of precipitate formation will eliminate the conventional steps required in removal of the undesired precipitate.